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Thread: possible subwoofer?

  1. #16
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    Quote Originally Posted by Lee in Montreal View Post
    The 40Hz peak is most likely room resonance. The 4560 doesn't go that low. According to JBL's own litterature, it has a useable range down to 50Hz. Not any lower.
    Similar though to a reflex cabinet, the speaker will continue to go low and chances are, will kill itself in the process. All the 4560's I ever used had something else under them with an active crossover so I never saw this sort of thing. I was thinking it was the Fs of the E145 because it would be a big coincidence if the room resonated at the same point. Maybe but the Mic close and run the test again.

    Allan.

  2. #17
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    Thanks for the input guys. Yeah, I also thought that the first peak and valley are room related more than anything...but I still want to attempt cutting off the 4560 at ~100hz and filling in below with some sort of sub...
    I will try the nearfield measurement when I get the mic back from my friend
    B

  3. #18
    Senior Member Lee in Montreal's Avatar
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    Quote Originally Posted by mantisory View Post
    Thanks for the input guys. Yeah, I also thought that the first peak and valley are room related more than anything...but I still want to attempt cutting off the 4560 at ~100hz and filling in below with some sort of sub...
    I will try the nearfield measurement when I get the mic back from my friend
    B
    Subs are to be used below 50Hz. Any higher than that, frequencies are directional and you will locate the source.

  4. #19
    Administrator Robh3606's Avatar
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    The 40Hz peak is most likely room resonance.
    That must be one hell of a high Q peak. You have to have enough energy from the speaker to energize the room mode. No energy no peak. Based on my expereince with them I am looking at the measurement and scrathing my head. Where is the broad peak above 100Hz from the short horn loading the driver?? It almost looks like the horn and the 145 are out of phase??

    You got me what's going on

    Rob
    "I could be arguing in my spare time"

  5. #20
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    If it helps, here is the response curve with the phase overlayed...I am pretty well a newbie and am not quite sure what's going on with it either. Although the phase response doesn't look all that out of line does it?

    Thanks for the help,
    Byron

  6. #21
    Senior Member pos's Avatar
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    you have to align the impulse response to remove the initial delay in order to have a readable phase response

  7. #22
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    Quote Originally Posted by pos View Post
    you have to align the impulse response to remove the initial delay in order to have a readable phase response
    Sorry, I am not sure what that means - this is the graph generated by REW with nothing added or anything by me...
    byron

  8. #23
    Senior Member Eaulive's Avatar
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    The phase response graph is generated by comparing the output of your speaker to a reference signal.
    Since the sound from your speaker obviously arrives to the processor a couple of ms later, you have to delay the reference signal by the same amount so the computing is correct.

    A correct phase graph should give you something like this:
    http://www.audioheritage.org/vbullet...l=1#post319731
    My avatar: 4520 loaded with 2225H on E140 frames,
    1x 2202H on custom front loaded horn, 2x 2426 on 2370.

  9. #24
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    The 40Hz peak is not a room-resonant, itīs the ports resonance. By changing port-area it can be moved around a little, but also affects low-end drop. The dip at ca 70Hz is also due to 4560īs design. One can expect acceptable frequency-responce(for hajfaj) from 100-125Hz. So go for a sub from just over 100Hz. If the 4560 is corner-placed it can be used a little lower though.

    If one reduces the chambervolume to ca 100dm3 instead of the original 220dm3, things begin to look really nice as the response gets straighter with the big dip and peaks smoothened out. We will be able to x/o against the sub at 60-70Hz.
    Brgds
    Lars

  10. #25
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    Quote Originally Posted by reVintage View Post
    The 40Hz peak is not a room-resonant, itīs the ports resonance. By changing port-area it can be moved around a little, but also affects low-end drop. The dip at ca 70Hz is also due to 4560īs design. One can expect acceptable frequency-responce(for hajfaj) from 100-125Hz. So go for a sub from just over 100Hz. If the 4560 is corner-placed it can be used a little lower though.

    If one reduces the chambervolume to ca 100dm3 instead of the original 220dm3, things begin to look really nice as the response gets straighter with the big dip and peaks smoothened out. We will be able to x/o against the sub at 60-70Hz.
    Thanks for the info Lars. I am not sure how I would go about reducing chamber volume. I think I am just going to go ahead with building a sub, either based on a 2245, or possibly a Tuba HT, and then cross over ~100Hz or so.
    B

  11. #26
    Administrator Robh3606's Avatar
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    If one reduces the chambervolume to ca 100dm3 instead of the original 220dm3, things begin to look really nice as the response gets straighter with the big dip and peaks smoothened out. We will be able to x/o against the sub at 60-70Hz.
    What software are you using to determine this?? Reducing the volume for the reflex portion will not give you a lower useable frequency limit with this driver. If anything you would need to increase the volume to extend it.

    Rob
    "I could be arguing in my spare time"

  12. #27
    Member reVintage's Avatar
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    Arrow

    Hey Rob,

    The hornreflexes(A7, 816, 4560, 4520 etc.) are very hard to handle as they are big compromises. You get shelving as as the horn has higher sensitivity. Also you get phase problems, giving dips between the horn and BR. As I remember Roediger has pointed this out earlier using the same software. But it will good enough with a higher XO. We have got quite good IRL results with 816/416 crossed at 350Hz to 200Hz LeCleach-horns.

    The only reliable software is Hornresp. See below, original first and then Pi*1,0(wall/floor). With 2205A as E145 has totally wrong parameters in JBLs list. Maybe E-140 is more like E-145, havenīt tried that, though.

    Highend response will be straight a tad higher up due to onaxis-response, the simmed are constant directivity. Note the 100dm3 version has a higher sensitivity in lowend almost eliminating the shelving.
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    Brgds
    Lars

  13. #28
    Senior Member grumpy's Avatar
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    IIRC, the error is for Vas, listed as 274.7 and should be ~427 (for E-145)

  14. #29
    Member reVintage's Avatar
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    Hey Grumpy,

    Thanks a lot, will do some new sims. Assumed it was VAS but didnīt care to use the std formulas to find out.

    By the way JBL are one of the few manufacturers that(normally) has correct T/S-parameters. Also Altec, but I have only compared their data of 414 and 416 with reality.

    EDIT: Had to try at once and now weīre talking! Original to the right, not so exiting, as expected. 100dm3 volume to the left. Sims are in 1*Pi= floor /wall placement.

    Both should be useful up against 800Hz on-axis. Maybe more if direct radiation works. Canīt be shown together with combined as above. Have simmed it with the directivity function though.

    With a 60-80Hz sub weīre home!

    Maybe one could cut the rear of the 4560 to reduce volume. We are very much alike Altec 816 now.
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    Brgds
    Lars

  15. #30
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    Ok, well, I think I am going to build a sub and x-over around 80Hz. With the Marchand XM44, I can get a number of 'frequency modules', so I will get one for 70 and 90hz as well, and go from there.
    Thanks for the help guys.
    As far as reducing the cabinet size, or removing the rear panel, etc, I am not sure how I'd proceed, so I will just use them as is...
    Byron

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